Evaporator tubes are utilized in a refrigeration unit for evaporating the coolant to produce the desired degree of cooling. Most evaporator tubes which depend on controlled gaps on powder metal surfaces have a common problem in that the tubes either flood the media reservoir or starve the replenishing of fluid. The commercial tubes available in the industry have varying pore sizes, but with only one pore size on the same fin. As a general rule, the prior art tubes are prepared by firming the outside of a tube to produce spiral grooves. Notches are cut into the fins at various intervals and, in some instances, some of the outer tips of the fins are folded over to contact the surface of the tube forming a passageway. The problem of efficient heat transfer tubing has been intensified because of environmental problems requiring the discontinuance of efficient refrigerants. As of this time, the newer refrigerants do not have the efficiency experienced by the banned refrigerants. Because of this variety of refrigerants, there is a need for a tube which can readily be adapted to a variety of different types of refrigerants.
U.S. Pat. No. 4,438,807, issued to Achint P. Mathur et al. on Mar. 27, 1984, discloses a heat transfer tube which has some fins bent over and it creates openings dependent upon the internal ribs to form smaller fins on the external surface of the tubing above them, causing the bent over fins to have gaps consistent with the decreased fin height. The openings can only be present when there is an internal fin present at the location to supply sufficient metal. All of the openings are the same size. The geometry displayed in this patent does not function effectively. If tube material is sucked into the groove on the mandrel as explained in column 6, lines 7 to 10, then effective fin height is reduced for that section of the tube. Since the adjacent fin has not been moved forward or backward, the cavity opening is actually triangular in shape and not the diamond shape illustrated in FIG. 3 of this patent. Its existence must depend upon the difference in fin height between adjacent fin convolutions before they are bent over.
Japanese Patent No. 1-87036, dated Mar. 31, 1989 filed by Hisashi Nakayama, has holes and pores which are not integral to the fin material and, in additional, are material placed over the finned surface which is then holed using an electrode which burns the circular hole through the overlaid material only after rollover. In order for that system to work, the rolled over fins cannot be completely rolled over to touch the adjacent fin, otherwise the tunnel is completely enclosed and the electrode is only stated to melt the "low conductive material."
Japanese Patent No. 63-172892, dated Jul. 16, 1988 issued to Hiromi Hashimoto, discusses tunnel cavities of an equal cross sectional area (tunnel 12 being larger than tunnel 8) which causes the rolled over fins to not completely touch along the outside diameter circumference. Further, all notches are of the same size. This patent places pores of the same size in groups as increasing heat flux to the surface will tend to activate single, broad portions of the tube's surface for nucleate boiling since refill pores are farther away. In addition, it has been found that broad groups of pores of the same size will effectively starve many of the activated pores of refrigerant, such that not all of the pores in the activated area will be available for nucleate boiling. This effect shows up as gaps and low values in the tube's nucleate boiling performance. Placing many pores of the same size in groups as increasing heat flux is supplied to the surface will tend to only activate single, broad portions of the surface of the tube for nucleate boiling since refill pores are further away. This effect in real terms will appear as gaps and low values in the nucleate boiling performance of the tube.
U.S. Pat. No. 4,059,147 issued to Thorne is similar to Mathur in that the notches or recesses are of uniform shape.